This invention relates to a process for spinning high strength, high modulus aromatic polyamide filaments, particularly at high, commercially desirable spinning speeds.
A process for preparing high strength, high modulus, aromatic polyamide filaments is known from U.S. Pat. No. 3,767,756 whereby highly anisotropic acid solutions of aromatic polyamides whose chain extending bonds are either coaxial or parallel and oppositely directed (para-aramids) are extruded through a spinneret into a layer of inert, non-coagulating fluid into a coagulating bath and then along with overflowing coagulant through a vertical spin tube aligned with the spinneret. Improved results are obtained if the entrance of the spin tube is provided with a deflecting ring as described in U.S. Pat. No. 4,078,034.
The process of U.S. Pat. No. 3,767,756 provides high strength, high modulus filaments of aromatic polyamides such as poly(p-phenylene terephthalamide) which are useful in the construction of vehicle tires, industrial belts, ropes, cables, ballistic vests, protective clothing and other uses.
For high spinning speeds, particularly when the denier of the yarn spun is of the order of 1500 denier or more, U.S. Pat. Nos. 4,298,565 and 4,340,559 provide an improvement over the spinning processes of U.S. Pat. Nos. 3,767,756 and 4,078,034. In accordance with the process of U.S. Pat. No. 4,298,565, the tenacity of the resulting filaments and yarn is increased, usually by a desirably significant amount of at least 1 gram/denier (gpd) (0.88 dN/tex) at a given spinning speed greater than 250 m/min. U.S. Pat. No. 4,298,565 discloses a spinning process in which additional coagulating liquid is jetted downwardly symmetrically about the filaments and travels down the spin tube with the overflowing coagulating liquid. The flow rates of the jetted and overflowing coagulating liquid are maintained constant and the momentum ratio of the jetted to the overflowing liquids being between 0.5 to 6.0. In addition, U.S. Pat. No. 4,298,565 teaches a mass flow rate of total coagulating liquid from 70 to 200 times the mass flow rate of the filaments. U.S. Pat. No. 4,340,559 discloses a spinning process also providing improvements in the high-speed spinning of para-aramid yarns. U.S. Pat. No. 4,340,559 teaches the use of a shallow bath providing substantially horizontal, nonturbulent flow of coagulating liquid toward an orifice for removal of coagulating liquid and fibers. The bath has no more than a minor portion of the coagulating liquid lower than the entrance of the bath orifice.